1. Field of the Invention
The present invention relates to an inkjet printing apparatus that prints images on a print medium using colored ink and image enhancing liquid.
2. Description of the Related Art
In recent years, inkjet printing apparatuses that use pigmented ink capable of obtaining high image fastness properties have become popular. However, there are many kinds of pigmented ink for which penetration of color into the print medium is difficult, and there is a tendency for pigment to remain on the surface of the print medium. Therefore, particularly in dark areas where a large amount of ink is used, the glossiness on the surface due to the remaining pigment is greater than necessary, and in some cases it may not be possible to obtain a desired color reproduction range.
In regards to this problem, Japanese Patent Laid-Open No. 2011-218564, for example, discloses a method that adjusts the reflected light on the print medium to a suitable amount and increases the color reproduction range by applying an image enhancing liquid to the printing surface after color pigmented ink is printed in dark areas where a large amount of ink is used.
However, as a result of diligent investigation performed by the inventors, it was found that when multi-pass printing is performed using a printing method such as disclosed in Japanese Patent Laid-Open No. 2011-218564, there are cases in which gloss unevenness appeared by band unit of the image. The mechanism by which this kind of gloss unevenness occurs will be explained below.
Typically, in multi-pass printing, line irregularity and density unevenness that appear in an image are reduced by having the printing head print in an image area that can be printed in one printing scan using a plurality of printing scans sandwiching conveyance operations of the print medium. However, in multi-pass printing, when there is a printing position displacement among a plurality of printing scans due to conveyance error of the print medium or a variation of distance between the print head surface and print medium, there is a possibility of a change in the coverage of dots on the print medium.
For example, in the case of 2-pass multi-pass printing, a group of dots that is printed in the first scan and group of dots that is printed in the second scan normally have an exclusive and complementary relationship. However, when printing position displacement among these dot groups occurs, the complementary relationship is lost, two dots that are supposed to be exclusive overlap, and the coverage of dots on the print medium decreases. As a result, when the printed dots are image enhancing liquid for controlling the glossiness, the glossiness in the area (band) where the printing position displacement occurred becomes different than the other areas, and gloss unevenness can be seen.